This is compatible with a one-shot communication system, assuming a pre-distribution of the public key.

An advantage of Diffie-Hellman over RSA for generating Ephemeral Keys. Generating a new Diffie-Hellman a new Ephemeral Key key pair is extremely fast (provided that some "DH parameters", i.e. the Diffie-Hellman Group into which DH is computed, are reused, which does not entail extra risks, as far as we know). This is not a really big issue for big servers, because a very busy TLS server could generate a new "ephemeral" RSA key pair every ten seconds for a very small fraction of his computing power, and keep it in RAM only, and for only ten seconds, which would be enough for Perfect Forward Secrecy.